The present invention relates to an anti-lock hydraulic brake system and more particularly to an anti-lock hydraulic brake system which reduces noise resulting from pressure surges utilizing a pressure fluid collecting means and a selector valve connected to the suction side of the pump. This system includes a master cylinder and at least one wheel brake connected via a brake line to the master cylinder, a cut-off valve to close the master cylinder in relation to the pressure fluid circuit, a pressure-fluid collecting means connecting to the wheel brake, an outlet valve in the connection between wheel brake and pressure-fluid collecting means, and a pump communicating with its suction side to the pressure-fluid collecting means.
An anti-lock hydraulic brake system is known from GB 2 056 606 A disclosing a system in which the outlet valve is opened to decrease the pressure in the wheel brake so that pressure fluid can discharge into the pressure-fluid collecting means. The pressure-fluid collecting means is a low-pressure accumulator, the piston of which simultaneously functions as a valve member for the cut-off valve. As a result, the cut-off valve closes automatically when the low-pressure accumulator is charged. The pump delivers fluid from the low-pressure accumulator directly into the wheel brake. In other words, pressure control is effected by one valve only. Although this affords ease of actuation, control functions are limited at the same time. More particularly, no pressure-retaining phase can be realized.
Admittedly, it is known to provide another valve, a so-called inlet valve, in the connection between the pump and the wheel brake to disconnect the wheel brake from pressure-fluid delivery. However, it has been shown that a great deal of switching noise results from the operation of this inlet valve. The price for the enhanced ease of actuation is the augmentation of noise emission from the system.